Blueberry bud mite

(Acariformes: Eriophyidae)

Blueberry bud mite, Acalitus vaccinii, is one of the world’s most serious pests on blueberries. It is native to North America. The first appearance of the blueberry bud mite in South Africa was reported in 2012, in the Mpumalanga province. This was the first time this pest was reported outside North America. Blueberry bud mite is very host specific, with blueberries being the main host plant. The possibility of a wider host range, other than Vaccinium spp. (lowbush, highbush and rabbiteye blueberries) is unlikely. Eriophyes vaccinii is a synonym of blueberry bud mite.

Nozibusiso Maphumulo

IPM-PROGRAMME, NORTH-WEST UNIVERSITY, POTCHEFSTROOM

Blueberry bud mite classification:

Class: Arachnida (spiders and mites) Order: Acariformes (mites) Family: Eriophyidae Genus: Acalitus Species: vaccinii

Blueberry bud mite has four life stages that occur together in large clusters. It reproduces rapidly inside the scales of the blueberry bud. Females lay up to 200 eggs in the bud scales. Nymphs start feeding just after hatching and reach sexual maturity within 15 days. Adult mites then migrate down the stem where they feed and move further into the centre of the buds where they become well established as the population increases. They survive on the inner buds of blueberries from autumn to spring and have multiple generations per year.

Blueberry bud mites are microscopic in size, ranging from 0,1 to 0,3 mm long and difficult to identify. Eggs are typical spherical mite eggs with a length of 0,055 mm and a width of 0,035 mm. They are clear to slightly whitish and translucent in colour. Protonymphs (first larval stage) are about 0,1 mm long, with a width of 0,035 mm, rectangular in shape, transparent and clear to whitish in colour. Deutonymphs (second larval stage) are about 0,15 mm long (Fig. 1) and of similar shape and colour. Adults are about 0,2 mm long, translucent to whitish and light cream-brown in colour with an elongated worm-like annulated body (Fig. 2). They only have two pairs of legs.

Blueberry bud mite is currently considered as one of the first serious and economically important arthropod pests of blueberries in South Africa and threatens blueberry production in the country. However, the threat differs depending on climate and the susceptibility of various cultivars.

Feeding damage to buds may be observed in spring when populations are high. Infestations can be detected by sam-

Figure 1: Deutonymph of blueberry bud mite under microscope (Keifer, 1939).

Figure 2: Blueberry bud mites in a flower bud bract (Craemer, 2018).

Figure 3: Rosette-like flower galls caused by blueberry bud mites on a blueberry plant (Craemer, 2018).

pling the current-season growth after harvest and dissecting floral buds next to the shoot tips, using a microscope to see the small mites. Feeding symptoms are noticeable in the spring by blistering on the outside bud scales and poor flower set. Poor plant growth and fruit set, mostly in the top parts of plants may be observed during summer.

Other feeding damage symptoms include galls (Fig. 3), an abnormal felty growth of hairs from the leaf epidermis, leaf curling, witches broom and bud malformation.

Control of mites can be challenging because they are protected from pesticides by bud scales. There are no pesticides registered for the control of blueberry bud mite since it is a new pest in South Africa. Cultural control practices such as pruning older branches and removing infected branches can be applied.

Predators of the blueberry bud mite are not known in South Africa. Therefore, biological control cannot be an option, especially because it has not been studied. Enquiries: mashimanenozi03@gmail.com